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## #1 2006-01-28 09:05:00

ineedhelp
Member
Registered: 2006-01-21
Posts: 7

### check my homework

I have two homework problems that I'm not sure I got right.  If someone could tell me if my answer is correct that would be great.  If its not right, i'll try to solve it again.

Suppose the sales of a particular brand of appliance satisfy the relationship: S(x) = 140x + 100 where S(x) represents the number of sales in year x, with x = 0 corresponding to 1982. Find the number of sales in 1987.

S(x) = 140(5) + 100
I came up with Sales in 1987 were 800.

Decide whether the pair of lines is parallel, perpendicular, or neither: the line through (3, -5) and (-1, 7) and the line through the points (6, -13) and (-2,11)

The first line slope is 2/2 and and the second line slope is -2/4. I came up with neither, because the the slope would be the same if parallel or reciprocal if perpendicular.  In this case they are niether.

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## #2 2006-01-28 09:50:46

mathsyperson
Moderator
Registered: 2005-06-22
Posts: 4,900

### Re: check my homework

In the second one, the gradients need to be calculated differently.

Between (3, -5) and (-1, 7), there is a gradient of

Similarly, between (6, -13) and (-2, 11), there is a gradient of

They have the same gradient and so are parallel.

Why did the vector cross the road?
It wanted to be normal.

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## #3 2006-01-28 10:23:39

MathsIsFun
Registered: 2005-01-21
Posts: 7,659

### Re: check my homework

And the computer can give you a little help with the straight line graph calculator

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..."  - Leon M. Lederman

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## #4 2006-01-28 11:05:32

mikau
Member
Registered: 2005-08-22
Posts: 1,504

### Re: check my homework

What the heck is gradients? Oddly my mathbook never mentioned that term.

A logarithm is just a misspelled algorithm.

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## #5 2006-01-28 11:29:12

ineedhelp
Member
Registered: 2006-01-21
Posts: 7

### Re: check my homework

mathsyperson wrote:

In the second one, the gradients need to be calculated differently.

Between (3, -5) and (-1, 7), there is a gradient of

Similarly, between (6, -13) and (-2, 11), there is a gradient of

They have the same gradient and so are parallel.

I see my mistake. I did 7-5 and -1+3 to get 2/2 and 11-13 and -2+6 to get -2/4. I'll fix it. Thanks.

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## #6 2006-01-28 11:55:16

mathsyperson
Moderator
Registered: 2005-06-22
Posts: 4,900

### Re: check my homework

mikau wrote:

What the heck is gradients? Oddly my mathbook never mentioned that term.

A gradient is just the slope of a line. Well, it's actually the slope of a curve at a given point, but it's most commonly applied to lines. It's basically an less technical way of saying dy/dx.

Why did the vector cross the road?
It wanted to be normal.

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